FILICES 



73 



apical portion, and they then assume a great variety of shapes — circular, 

 reniform, crescent-shaped, linear, or they are concealed beneath the 

 revolute margin of the leaf The sorus may or may not be covered by 

 a membrane called the indusium, an outgrowth of the epiderm. In the 



Fig. iT..—Asplentum Adianium-nigrum L. ; rhizome, with fronds showing circinate 

 vernation (natural size), a, under side of fertile pinnule (magniiied). 



Cyatheaceae they assume the form of a cup ; in the Hymenophyllace» 

 they are situated at the extremity of a vein at the apex or margin t3f a 

 pinna. In some . instances, as in our native 'flowering ' or ' royal fern ' 

 .(Osmunda regalis, L.), the sori completely consume, in the course of their 



